Feature/worldboss fe qa 4

[eugene-doobu]

This pull request includes several changes to the WorldBossReward and WorldBossSeasonReward classes to improve the handling of null states and update reward calculations. The most important changes include adding null checks, modifying error messages, and updating damage display logic.

Improvements to null state handling:

• nekoyume/Assets/_Scripts/UI/Module/WorldBoss/WorldBossReward.cs: Added a null check for preRaiderState to ensure notifications are set correctly and avoid potential null reference exceptions.
• nekoyume/Assets/_Scripts/UI/Module/WorldBoss/WorldBossSeasonReward.cs: Added a null check for worldBossState in the Set method to handle cases where worldBossState might be null and to modify the error message accordingly.

Updates to reward calculations and display:

• nekoyume/Assets/_Scripts/UI/Module/WorldBoss/WorldBossSeasonReward.cs: Updated the logic to display worldBossTotalDamage and userTotalDamage correctly, ensuring that worldBossTotalDamage is set before checking if raider is null.
• nekoyume/Assets/_Scripts/UI/Module/WorldBoss/WorldBossSeasonReward.cs: Removed redundant setting of worldBossTotalDamage when raider is null and streamlined the damage display logic.

Miscellaneous changes:

• nekoyume/Assets/_Scripts/UI/Module/WorldBoss/WorldBossSeasonReward.cs: Changed the condition to check if the calculated amount is greater than zero using Math.Floor to avoid potential issues with floating-point precision.
• nekoyume/Assets/_Scripts/UI/Module/WorldBoss/WorldBossSeasonReward.cs: Added the System namespace import for better handling of mathematical operations.